Modern audio codecs consists of multiple compression schemes optimized for signals with different properties. With practically no exception, speech-like signals are processed with time-domain codecs, while music signals are processed with transform-domain codecs. Coding schemes that are supposed to handle both speech and music signals require a mechanism to recognize whether the input signal comprises speech or music, and switch between the appropriate codec modes. Such a mechanism may be referred to as a speech-music classifier, or discriminator. An overview illustration of a multimode audio codec using mode decision logic based on the input signal is shown in FIG. 1a. 
In a similar manner, among the class of music signals, one can discriminate more noise like music signals from harmonic music signals, and build a classifier and an optimal coding scheme for each of these groups. This abstraction of creating a classifier to determine the class of a signal, which then controls the mode decision is illustrated in FIG. 1b. 
There are a variety of speech-music classifiers in the field of audio coding. However, these classifiers cannot discriminate between different classes in the space of music signals. In fact, many known classifiers do not provide enough resolution to be able to discriminate between classes of music in a way which is needed for application in a complex multimode codec.